A Study of Soil Bioassay Technique Using Prometryne

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Abstract
A cooperative study to evaluate the accuracy and precision of bioassays was carried out among investigators at several locations for 3 years. Oats (Avena sativaL., var. Cimarron) seedlings were used as indicator plants for soil-applied 2,4-bis-(isopropylamino)-6-methylthio-s-triazine [prometryne]. Assay results varied a great deal initially, and ranged from 147% below to 234% above the prometryne actually applied. The adoption of uniform conditions and procedures greatly increased the uniformity of the determinations between locations to a range of from 37% low to 0% high in prometryne applied. Chemical analyses of the soils ranged from 13% low to 20% high. Measurements of herbicidal activity included dry and fresh plant weights, plant height, visual injury ratings, and plant water use. The average concentration of prometryne in the soil as estimated with several types of measurements gave a much better measure of prometryne content than any one measurement alone. Prometryne rapidly and greatly affected the utilization of water by oats seedlings and careful measurement of water use showed potential of being a good early indicator of prometryne activity.